Kinetics of boron hydrolysis for hydrogen production

This study examines the kinetics of boron hydrolysis. The boron hydrolysis reaction is classified as a noncatalytic heterogeneous reaction. It was found the steam rapidly hydrolyzes the boron, forming an oxide ash layer that then also reacts with the steam, forms gaseous boric acid, and re-exposes the boron substrate to steam. Additionally, the thickness of the ash layer, once formed, was found to be relatively constant through the reaction. In order to facilitate kinetic analysis the reaction was divided into two stages: a fast oxidation stage and a second, slower stage. The corresponding kinetic parameter for the first stage activation energy is 25 kJ/mol. The shrinking core model was used to model the second stage of the hydrolysis reaction where it was found that diffusion of steam through the ash layer was the rate limiting step.

► Complete hydrolysis of boron. ► Hydrolysis activation energy is 25 kJ/mol. ► Complete boron oxide gasification. ► Gas diffusion through the oxide layer was the hydrolysis limiting step. ► Shrinking Core Model applies for the boron hydrolysis in the presence of B2O3.